The research that is being proposed shall represent the third phase of an ongoing project which has as its immediate and primary goal the demonstration of the neuronal organization of the rabbit's central visual system and which has as its long-range goal the more thorough understanding of visual mechanisms as thse pertain to the mammals and evolutionary trends among the mammals. In its first phase this project has provided basic data on the patterns of neuronal inputs to thalamic, midbrain and pontine nuclei from the retina and from visual cortical areas I and II of Thompson, Woolsey & Talbot (1950) (Supported by grant NB 06253). In its second phase this project has yielded data on the general organization of corticocortical fiber connections (both the associational and the commissural connections) to visual cortical areas I and II of the rabbit (Supported by grant EY 00607). In the proposed research, the results obtained in the second phase shall be extended in that detailed information shall be sought on the precise origins and terminations of the corticocortical fiber projections in the rabbit. In addition, the proposed research shall include a study of the organization of fiber connections between the visual cortical areas and non-visual cortical areas of the rabbit. Just as with the first and second phases of this project, the proposed research shall consist of experiments in which discrete, small lesions are placed at various locations on the first or second visual cortical areas, and subsequent to this, the rabbits are killed and the patterns of the fiber degeneration then determined from serially sectioned brains prepared by the Nauta (and its modifications) and Nissl methods. However, in the proposed research an emphasis shall be placed upon the detailed, precise determination of origins and terminations for cortical fiber connections utilizing the technique of autoradiography as set down by Cowan et al. (Brain Res.,37: 21-51, 1972). In summary, the research here proposed shall combine the use of the fiber degeneration methods, as well-established in this laboratory, with the use of autoradiography, currently underway in this laboratory. BIBLIOGRAPHIC REFERENCES: Giolli, R.A., L.C. Towns and D.A. Haste 1975 Corticocortical fiber connections of visual areas I and II in the rabbit. Anat. Rec., 181: 361.